1. Field of the Invention
The present invention relates in general to optical disk systems and in particular, to a flexible signal interface for use in an optical disk system and systems and methods using the same.
2. Description of the Related Art
Optical disks have been used for many years for the mass storage of digital data. Some well known examples of optical disks include digital audio compact disks (CD-DAs), compact disk read-only memories (CD-ROMs) and digital video disks (DVD-RAMs, xe2x88x92ROM, +RW, xe2x88x92RW, CD-R, CD-RWs). Essentially, digital data is stored on a plastic disk as a series of pits in the disk surface. During playback, a beam of light is directed to the rotating disk surface and the intensity of the photons reflected from the pits measured. A modulated electrical signal is generated that can be processed and the data stored on the disk recovered.
A basic configuration for the read (playback) mechanism has developed over a number of years. This configuration includes a pickup or sled which is movable so that a laser, a lens, and array of photodiodes can be positioned directly over the data being read off of the disk. As the disk turns, the photons from the laser are reflected off the pits and received by the photodiodes which generate electrical signals having a current that is proportional to photon density.
The multiple signals output from the photodiodes represent both data detection and servo alignment information. The summation of the high speed data channel signal, which may be composed of the signals A+B+C+D from an astigmatic photodiode array, results in a composite signal with relevant information between approximately 10 KHz and 60 MHz for current DVD players. Servo information contained in these signals however, is at frequencies less than 1 MHz (for current spindle rotation rates of  less than 6000 RPM). Because of these information rates, the data channel signal is sometimes AC-coupled to the data detection and summation circuitry mounted on an accompanying stationary circuit board. Otherwise, some degradation of the dynamic range must be accepted due to the dc content of the incoming signal.
The typical current signal generated by a photodiode is on the order of 1 uA. Transferring this signal directly down a flexible cable to the stationary circuit board therefore would seriously degrade the signal to noise ratio. Hence, transimpedance amplifiers, which convert the current from the photodiode array into a voltage for driving the cable, are mounted in the pickup to minimize noise and interference effects. The data detection, error correction, and servo systems are kept off of the pickup not only because the same interference reasons, but primarily to reduce the physical size and mass of the sled. These systems are mostly digital and switching noise on the pickup may degrade the signal to noise ratio.
There are several different types of optical pickups which are employed depending on the system configuration and performance requirements. Legacy issues also arise with newer systems which require the use of specific pickup for backwards compatibility with older technologies. For example, it may be necessary in a DVD system to use a pickup which is also capable of retrieving data from CD and CD-ROM so that one system can handle all three types of information.
Different types of pickups output different sets of signals. For example, some pickups will combine the high frequency data signals output from the photodiode array for transmission to the fixed processing circuitry as a single signal RF, while other pickups transmit these signals individually. Moreover, some pickups output data and servo control information differentially while others transmit signals in a single-ended fashion, Additionally, some pickups are only used for DVD disks, others for only CD disks, as some for both DVD and CD disks.
Currently, the front-end devices in the fixed processing circuitry are normally customized to be compatible with one, or at least only a very few, types of pickups. This reduces the flexibility of both the system and the pickups, since for the most part they are not freely interchangeable. Hence, what is needed is a flexible way of interfacing different optical pickups with the corresponding fixed processing circuitry.
An interface is disclosed for interfacing an optical pickup with associated processing circuitry. A plurality of inputs receive data retrieved from an optical disk by the pickup and a plurality of signal paths, each coupled to a corresponding one of the inputs are independently activated and deactivated to selectively pass the data to the processing circuitry. This reconfigurability is done without sacrificing bandwidth.
Embodiments of the present inventive concepts provide a flexible way of allowing a single device or chip to be compatible with different types of optical pickups. These pickups can support differing numbers of output channels, signal summing for different data types (e.g. DVD and CD data).